1. Field of the Invention
The present invention relates to digital recording and/or playback, and more particularly, to a variable speed playback method and apparatus for controlling a fast transfer operation and a normal speed playback operation without reconstructing and recording separate data for variable speed playback.
2. Description of the Related Art
A digital video cassette recorder (VCR) is an example of a digital recording and playback apparatus. A recording medium used in the digital VCR is separately assigned an area in which normal speed playback data is recorded and an area in which variable speed playback (which can be referred to as trick play) data is recorded. This is for performing variable speed playback without influencing normal speed playback by recording separate data only for the variable speed playback in a position which is traced by a playback head and by playing back the separate data.
FIG. 1 is a block diagram of a conventional digital VCR which separately records normal speed playback data and variable speed playback data as described above. The conventional digital VCR includes a separate encoder 104 and a separate decoder 118 for variable speed recording and playback, respectively, in addition to an encoder 102 and a decoder 116 for normal speed recording and playback, respectively.
The normal speed recording data encoder 102 converts an input Moving Picture Experts Group (MPEG)-2 bit stream into data, which can be recorded in a digital VCR, and provides the data to a multiplexer (MUX) 106. The variable speed recording data encoder 104 recompresses an intra picture which is extracted from the input MPEG-2 bit stream to generate recording data for variable speed playback and provides the recording data to the multiplexer 106.
The multiplexer 106 time-division multiplexes the recording data for normal speed playback, which is provided from the normal speed recording data encoder 102, and the recording data for variable speed playback, which is provided from the variable speed recording data encoder 104, and provides the output thereof to a recording signal processor 108. The recording signal processor 108 includes a recording amplifier and a channel modulator and error correction code (ECC) encoder, and generates an error correction coded bit stream. The error correction coded bit stream is recorded in a recording medium 112 in the form of a magnetic signal through an electricity/magnetism transducer 110.
The normal speed recording data and the variable speed recording data, which are separately recorded in a recording medium, are played back as follows according to a normal speed playback mode and a variable speed playback mode, respectively. Primarily, a signal which is read from the recording medium 112 is provided in the form of an electrical signal to a playback signal processor 114 via the electricity/magnetism transducer 100. The playback signal processor 104 includes a playback amplifier, an equalizer and a channel demodulator and ECC decoder, and provides an error correction decoded bit stream to both the normal speed playback data decoder 116 and the variable speed playback data decoder 118.
The normal speed playback data decoder 116 decodes the error correction decoded data for only normal speed playback and provides decoded data to a demultiplexer (DEMUX) 120. The variable speed playback data decoder 108 decodes the error correction decoded data for only variable speed playback and provides decoded data to the demultiplexer 120. In response to a normal/variable speed playback mode signal NORMAL/TRICK, the demultiplexer 120 outputs only a normal speed playback signal, which is decoded by the normal speed playback data decoder 116, in a normal speed playback mode and outputs only a variable speed playback signal, which is decoded by the variable speed playback data decoder 118, in a variable speed playback mode, thereby allowing normal speed playback or variable speed playback.
The variable speed recording data encoder 104 of the conventional digital VCR extracts only necessary data for variable speed playback from input normal speed recording data. Since sufficient recording area is not assigned to variable speed playback data, the variable speed playback data must be compressed for recording. Accordingly, picture quality can be degraded due to loss of information and excessive compression. Moreover, the conventional technology needs the separate encoder and decoder for variable speed recording and playback in addition to the encoder and decoder for normal speed recording and playback, thereby complicating the structure and increasing the cost.
To solve the above problems, it is an objective of the present invention to provide a variable speed playback method for controlling a fast transfer operation and a normal speed playback operation without reconstructing and recording separate data for variable speed playback.
It is another objective of the present invention to provide a variable speed playback apparatus for controlling a fast transfer operation and a normal speed playback operation without reconstructing and recording separate data for variable speed playback.
Accordingly, to achieve the above objectives, there is provided a variable speed playback method for helical scanning and playing back digital data stored in a recording medium. Fast transfer operation is performed on the recording medium in response to a variable speed mode. The variable speed mode is selected by a user interface. Data stored in the recording medium is played back at a normal playback speed after the fast transfer operation. Therefore, the fast transfer operation and the normal playback operation are repeatedly performed, thereby realizing variable speed playback.
To achieve the above objectives, there is also provided a variable speed playback apparatus for helically scanning and playing back digital data stored in a recording medium. The apparatus includes a transfer unit for moving the recording medium, a controller for controlling the transfer unit so as to repeatedly perform a fast transfer operation for moving the recording medium at a high speed and a normal playback operation for playing back the data of the recording medium at a normal playback speed after the fast transfer operation, and a restoring unit for reconstructing data, which is read from the recording medium during each period of the normal playback operation, to at least one picture of display data.